ABSTRACT
New sheet flow experiments using massive plastic particles are presented in this paper. The Shields number and suspension number values are set to 0.45 and close to unity, respectively. An acoustic high-resolution profiler (ACVP, Hurther et al. 2011 ) has been used to measure the colocalized streamwise and wall normal velocities between the non-moving sediment bed to the free surface with a vertical resolution of 3mm and a measurement rate of 78Hz. Ensemble averaging over several identical experimental runs guaranty converged streamwise velocity, turbulent shear stress and intensity profiles. The analysis addresses the physical processes underlying the transport of sediments in the dense nearbed layer. In particular, using dimensional arguments, it is shown that the inflection point observed in the streamwise velocity profile corresponds to a minimum in the mixing length profile. It is believed that below this point the rheology is dominated by granular interactions whereas above it the rheology is dominated by turbulent processes. In this region a logarithmic layer is shown to exist with a corresponding von Karman parameter which is considerably reduced compared to the clear water value.
